Control device, system, and control method

ABSTRACT

To estimate a positional relationship between devices having transmitted and received signals with higher accuracy.A control device includes a control unit that compares reliability parameters that are indexes indicating a degree of whether or not a signal is appropriate as a processing target for estimating a positional relationship between each of the plurality of communication devices and the other communication device, calculated on the basis of the signals received from the other communication device by the communication device, and performs control for estimating the positional relationship on the basis of a signal transmitted and received between the communication device that has received a signal that is more appropriate as a processing target for estimating the positional relationship and the other communication device.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is based upon and claims benefit of priority fromJapanese Patent Application No. 2021-143138, filed on Sep. 2, 2021, theentire contents of which are incorporated herein by reference.

BACKGROUND

The present invention relates to a control device, a system, and acontrol method.

In recent years, a technique for estimating a positional relationshipbetween devices according to results of transmitting and receiving awireless signal between devices has been disclosed. For example,International Publication No. WO2015/176776 discloses a technique inwhich an ultra-wideband (UWB) receiver estimates an incidence angle of asignal from a UWB transmitter by using a UWB signal.

SUMMARY

However, the technique disclosed in International Publication No.WO2015/176776 has a problem that even though the accuracy of estimationof an incidence angle of a signal may decrease in an environment such asthat with the presence of shielding between transmission and reception,no measures thereagainst are taken.

Therefore, the present invention has been made in view of the aboveproblem, and an object of the present invention is to provide a noveland improved control device, system, and control method capable ofestimating a positional relationship between devices that transmit andreceive a signal with higher accuracy.

To solve the foregoing problem, according to an aspect of the presentinvention, there is provided a control device comprising: a control unitthat performs control for estimating a positional relationship between aplurality of communication devices each having three or more antennasand another communication device on the basis of signals transmitted andreceived between the plurality of communication devices and the othercommunication device, wherein the control unit compares reliabilityparameters that are indexes indicating a degree of whether or not asignal is appropriate as a processing target for estimating a positionalrelationship between each of the plurality of communication devices andthe other communication device, calculated on the basis of the signalsreceived from the other communication device by the communicationdevice, and performs control for estimating the positional relationshipon the basis of a signal transmitted and received between thecommunication device that has received a signal that is more appropriateas a processing target for estimating the positional relationship andthe other communication device.

To solve the foregoing problem, according to another aspect of thepresent invention, there is provided a system comprising: a plurality ofcommunication devices each of which has three or more antennas; anothercommunication device that has one or more antennas; and a control devicethat performs control for estimating a positional relationship betweenthe plurality of communication devices and the other communicationdevices on the basis of signals transmitted and received between theplurality of communication devices and the other communication devices,wherein the control device compares reliability parameters that areindexes indicating a degree of whether or not a signal is appropriate asa processing target for estimating a positional relationship betweeneach of the plurality of communication devices and the othercommunication device, calculated on the basis of the signals receivedfrom the other communication device by the communication device, andperforms control for estimating the positional relationship on the basisof a signal transmitted and received between the communication devicethat has received a signal that is more appropriate as a processingtarget for estimating the positional relationship and the othercommunication device.

To solve the foregoing problem, according to another aspect of thepresent invention, there is provided a control method executed by acomputer, comprising: transmitting and receiving signals between aplurality of communication devices each of which has three or moreantennas and another communication device; and performing control forestimating a positional relationship between the plurality ofcommunication devices and the other communication device on the basis ofthe transmitted and received signals, wherein the performing control forestimating a positional relationship between the plurality ofcommunication devices and the other communication device includescomparing reliability parameters that are indexes indicating a degree ofwhether or not a signal is appropriate as a processing target forestimating a positional relationship between each of the plurality ofcommunication devices and the other communication device, calculated onthe basis of the signals received from the other communication device bythe communication device, and performing control for estimating thepositional relationship on the basis of a signal transmitted andreceived between the communication device that has received a signalthat is more appropriate as a processing target for estimating thepositional relationship and the other communication device.

As described above, according to the present invention, it is possibleto estimate a positional relationship between devices that transmit andreceive a signal with higher accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an example of a configuration ofa system 1 according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram for describing an outline example ofthe system 1 according to the present embodiment.

FIG. 3 is a diagram illustrating an example of a communicationprocessing block of a communication unit 220 according to the presentembodiment.

FIG. 4 is a graph illustrating an example of CIR according to thepresent embodiment output from an integrator 229.

FIG. 5 is a diagram illustrating an example of a communicationprocessing block of the communication unit 220 according to the presentembodiment.

FIG. 6A is an explanatory diagram for describing an example of a weightparameter calculation method according to a first specified value.

FIG. 6B is an explanatory diagram for describing an example of a weightparameter calculation method using a linear function as a specifiedfunction.

FIG. 6C is an explanatory diagram for describing an example of a weightparameter calculation method using a trigonometric function as aspecified function.

FIG. 6D is an explanatory diagram for describing an example of a weightparameter calculation method using an exponential function as aspecified function.

FIG. 7A is an explanatory diagram for describing an example of a weightparameter calculation method according to the first specified value.

FIG. 7B is an explanatory diagram for describing an example of a weightparameter calculation method using a linear function as a specifiedfunction.

FIG. 7C is an explanatory diagram for describing an example of a weightparameter calculation method using a trigonometric function as aspecified function.

FIG. 7D is an explanatory diagram for describing an example of a weightparameter calculation method using an exponential function as aspecified function.

FIG. 8 is an explanatory diagram for describing an example of anoperation process of the system 1 related to Example 1.

FIG. 9 is a block diagram illustrating a configuration example of avehicle 20 related to Example 2 and Example 3.

FIG. 10 is an explanatory diagram for describing a control example ofthe system 1 related to Example 2.

FIG. 11 is an explanatory diagram for describing an example of anoperation process of the system 1 related to Example 2.

FIG. 12 is an explanatory diagram for describing a control example ofthe system 1 related to Example 3.

FIG. 13 is an explanatory diagram for describing another control exampleof the system 1 related to Example 3.

FIG. 14 is an explanatory diagram for describing an example of anoperation process of the system 1 related to Example 3.

DETAILED DESCRIPTION OF THE EMBODIMENT(S)

Hereinafter, a preferred embodiment of the present invention will bedescribed in detail with reference to the accompanying drawings. In thepresent specification and the drawings, constituents havingsubstantially the same functional configuration are given the samereference numerals, and thus repeated description will be omitted.

In the present specification and the drawings, constituents havingsubstantially the same functional configuration may be distinguished byadding different letters or numbers after the same reference numeral.For example, a plurality of constituents having substantially the samefunctional configuration are distinguished as necessary, such asin-vehicle devices 200-1 and 200-2. However, in a case where it is notnecessary to particularly distinguish a plurality of constituents havingsubstantially the same functional configuration as each other, only thesame reference numeral is given. For example, in a case where it is notnecessary to distinguish between the in-vehicle devices 200-1 and 200-2,they are simply referred to as the in-vehicle device 200.

1. Configuration Example

FIG. 1 is a block diagram illustrating an example of a configuration ofa system 1 according to an embodiment of the present invention. As shownin FIG. 1 , the system 1 according to the present embodiment includes aportable device 100, an in-vehicle device 200, a control device 300, andan operation device 400.

The in-vehicle device 200, the control device 300, and the operationdevice 400 according to the present embodiment are mounted on a vehicle20. The vehicle 20 is an example of a moving object, and is, forexample, a vehicle licensed by a user (for example, a vehicle owned bythe user or a vehicle temporarily rented to the user). A moving objectaccording to the present embodiment includes not only the vehicle 20 butalso an aircraft, a ship, and the like.

Portable Device 100

The portable device 100 is an example of another communication device,and is a device carried by a user who is using the vehicle 20. Theportable device 100 may be an electronic key, a smartphone, a tabletterminal, a wearable terminal, or the like. As shown in FIG. 1 , theportable device 100 includes a control unit 110 and a communication unit120.

The control unit 110 controls the overall operation of the portabledevice 100. The control unit 110 causes the communication unit 120 totransmit, for example, a Poll (polling) signal that will be describedlater. The control unit 110 causes the communication unit 120 totransmit a Final signal that will be described later. The control unit110 is configured with, for example, electronic circuits such as acentral processing unit (CPU) and a microprocessor.

The communication unit 120 performs wireless communication with acommunication unit 220 included in the in-vehicle device 200. Forexample, the communication unit 120 transmits a Poll signal under thecontrol of the control unit 110. The communication unit 120 receives aResp (response) signal transmitted from the communication unit 220included in the in-vehicle device 200 as a response to the transmittedPoll signal. The communication unit 120 transmits a Final signal as aresponse to the received Resp signal under the control of the controlunit 110.

The wireless communication between the communication unit 120 and thecommunication unit 220 included in the in-vehicle device 200 is realizedby, for example, a signal compliant with ultra-wideband wirelesscommunication (hereinafter, referred to as a UWB signal).

In wireless communication using a UWB signal, in a case where an impulsemethod is used, it is possible to measure an air propagation time ofradio waves with high accuracy by using radio waves with a very shortpulse width of nanoseconds or less, and thus to perform positioning anddistance measurement based on the propagation time with high accuracy.The communication unit 120 is configured as, for example, acommunication interface capable of performing communication using a UWBsignal.

The UWB signal may be transmitted and received as a distance measurementsignal and a data signal. The distance measurement signal is any of aPoll signal, a Resp signal, and a Final signal transmitted and receivedin a distance measurement process that will be described later. Thedistance measurement signal may be configured in a frame format havingno payload portion for storing data, or may be configured in a frameformat having a payload portion. On the other hand, the data signal ispreferably configured in a frame format having a payload portion forstoring data.

The communication unit 120 has at least one antenna 121. Thecommunication unit 120 transmits and receives a wireless signal via atleast one antenna 121.

In-Vehicle Device 200

The in-vehicle device 200 is an example of a communication device and isa device mounted on the vehicle 20. As shown in FIG. 1 , the in-vehicledevice 200 includes a control unit 210 and a communication unit 220.

The control unit 210 controls the overall operation of the in-vehicledevice 200. The control unit 210 causes the communication unit 220 totransmit, for example, a Resp signal that will be described later. Thecontrol unit 210 is configured with, for example, electronic circuitssuch as a CPU and a microprocessor.

The communication unit 220 performs wireless communication with thecommunication unit 120 included in the portable device 100. Thecommunication unit 220 receives a Poll signal transmitted from thecommunication unit 120 included in the portable device 100. Thecommunication unit 220 transmits a Resp signal as a response to thereceived Poll signal under the control of the control unit 210. Thecommunication unit 220 receives the Final signal transmitted from thecommunication unit 120 included in the portable device 100 as a responseto the transmitted Resp signal.

The communication unit 220 has at least three or more antennas 221. Thecommunication unit 220 transmits and receives wireless signals via threeor more antennas 221. However, in a case where the control device 30according to the present invention is applied in Example 1 that will bedescribed later, the communication unit 220 needs to have at least fouror more antennas 221.

Control Device 300

The control device 300 performs control for calculating a positionalrelationship between the portable device 100 and the in-vehicle device200. As shown in FIG. 1 , the control device 300 includes acommunication unit 310 and a control unit 320. In the description of thepresent specification, an example in which the vehicle 20 according tothe present embodiment is configured by separating the in-vehicle device200 and the control device 300 will be described, but a function of thecontrol device 300 may be realized by the portable device 100 or thein-vehicle device 200.

The communication unit 310 uses any communication method to performvarious communications with the in-vehicle device 200. For example, thecommunication unit 310 receives information regarding a signaltransmitted and received between the portable device 100 and thein-vehicle device 200 from the communication unit 220 included in thein-vehicle device 200. Any communication method may be wiredcommunication or wireless communication. The communication unit 310 mayperform various communications with the communication unit 120 includedin the portable device 100 by using a wireless communication method.

The control unit 320 controls the overall operation of the controldevice 300. The control unit 320 performs control for estimating apositional relationship between the portable device 100 and thein-vehicle device 200 on the basis of, for example, a signal transmittedand received between the portable device 100 and the in-vehicle device200. As shown in FIG. 1 , the control unit 320 includes a parametercalculation unit 321 and a position estimation unit 325.

The control unit 320 is configured with, for example, electroniccircuits such as a CPU and a microprocessor.

The parameter calculation unit 321 calculates, on the basis of a signaltransmitted and received between the in-vehicle device 200 and theportable device 100, a reliability parameter that is an index indicatingthe degree of whether or not the signal is appropriate as a processingtarget for estimating a positional relationship between the portabledevice 100 and the in-vehicle device 200. Details of the reliabilityparameter will be described later.

The position estimation unit 325 estimates a positional relationshipbetween the portable device 100 and the in-vehicle device 200 on thebasis of the signal transmitted and received between the portable device100 and the in-vehicle device 200. For example, the position estimationunit 325 calculates a distance measurement value between the portabledevice 100 and the in-vehicle device 200 on the basis of the signaltransmitted and received between the portable device 100 and thein-vehicle device 200. The position estimation unit 325 estimates anarrival angle of a signal on the basis of the signal received from theportable device 100 by the in-vehicle device 200. The positionestimation unit 325 calculates a two-dimensional position or athree-dimensional position of the portable device 100 on the basis ofthe calculated distance measurement value and the arrival angle of thesignal. Various processes related to estimation of a positionalrelationship are executed by using the reliability parameter calculatedby the parameter calculation unit 321, and details thereof will bedescribed later.

Operation Device 400

The operation device 400 is a device that is operated under the controlof the control device 300. The operation device 400 may be a door key ofthe vehicle 20 or an engine of the vehicle 20.

The configuration example of the system 1 according to the presentembodiment has been described above. Subsequently, with reference toFIGS. 2 to 5 , technical features of the system 1 according to thepresent embodiment will be described.

2. Technical Features 2.1. Multipath Environment

In processes based on a signal transmitted and received between theportable device 100 and the in-vehicle device 200, the estimationaccuracy of a positional relationship may decrease depending on a radiowave propagation environment.

As an example of such a situation, there is a case where an object suchas a pillar is present in a communication path from the antenna 121 tothe antenna 221. In this case, for example, reception power of atransmitted and received signal may decrease, and thus the estimationaccuracy of a positional relationship may decrease.

Another example of such a situation is a situation in which multipathsoccur. The multipaths refer to a state in which a plurality of radiowaves transmitted from a certain transmitter (for example, thecommunication unit 120) reach at a receiver (for example, thecommunication unit 220), and occur in a case where a plurality of radiowave paths are present between the transmitter and the receiver. In asituation in which multipaths are occurring, radio waves passing througha plurality of different paths may interfere with each other, and thusthe estimation accuracy of a positional relationship may be reduced.

Therefore, a positional relationship between the portable device 100 andthe in-vehicle device 200 estimated by the position estimation unit 325may include an estimation error due to the multipath environment. Here,the control device 300 according to the present embodiment estimates apositional relationship between the portable device 100 and thein-vehicle device 200 by using a reliability parameter that is an indexindicating the degree of whether or not a signal is appropriate as aprocessing target for estimating the positional relationship between theportable device 100 and the in-vehicle device 200 calculated on thebasis of the signal received from the portable device 100 by thein-vehicle device 200. Thereby, the influence of an estimation error ofa positional relationship caused by the above multipath environment canbe reduced.

Hereinafter, an outline example of the system 1 according to the presentembodiment will be described with reference to FIG. 2 .

FIG. 2 is an explanatory diagram for describing an outline example ofthe system 1 according to the present embodiment. As shown in FIG. 2 ,the communication unit 120 included in the portable device 100 has theantenna 121. The communication unit 220 included in the in-vehicledevice 200 has, for example, an antenna 221A, an antenna 221B, anantenna 221C, and an antenna 221D as a four-element array antenna.However, the number of antennas included in the communication unit 120included in the portable device 100 and the communication unit 220included in the in-vehicle device 200 is not limited to the aboveexample. For example, the number of antennas of the communication unit120 may be a plural number, and the number of antennas 221 of thecommunication unit 220 may be five or more. In a case of applying thecontrol device 300 according to the present invention in Example 2 orExample 3 that will be described later, the communication unit 220 mayhave three antennas 221.

A scale ratio of the communication unit 220 and the plurality ofantennas 221 of the communication unit 220 is not limited to a scaleratio shown in the figure. For example, the antenna 221A, the antenna221B, the antenna 221C, and the antenna 221D may be arranged atintervals of about ½ wavelength, respectively. An arrangement shape ofthe four antennas may be a square shape, a parallelogram shape, atrapezoidal shape, a rectangular shape, and any other shape. However, itis desirable that the plurality of antennas 221 are arranged on a plane,not on the same straight line.

In FIG. 2 , the antenna 121 of the portable device 100 is disposed atthe upper left end of the portable device 100, but a dispositionposition of the antenna 121 of the portable device 100 is not limited tothe above example. For example, the antenna 121 may be disposed at anyposition in the portable device 100.

As shown in FIG. 2 , for example, the antenna 121 may transmit andreceive a signal S to and from at least one of the plurality of antennas221 of the communication unit 220.

The communication unit 310 included in the control device 300 receivesinformation regarding the signal S transmitted and received between theportable device 100 and the in-vehicle device 200 from either thecommunication unit 120 or the communication unit 220. Subsequently, theparameter calculation unit 321 may calculate a reliability parameter onthe basis of the transmitted and received signal S. The positionestimation unit 325 may estimate a positional relationship between theportable device 100 and the in-vehicle device 200 on the basis of thetransmitted and received signal S.

2.2. CIR Calculation Process

The communication unit 120 included in the portable device 100 and thecommunication unit 220 included in the in-vehicle device 200 accordingto the present embodiment may calculate a channel impulse response (CIR)indicating characteristics of a wireless communication path between thecommunication unit 120 and the communication unit 220.

The CIR in the present specification is calculated by one (hereinafter,also referred to as a transmission side) of the communication unit 120and the communication unit 220 transmitting a wireless signal includinga pulse and the other (hereinafter, also referred to as a receptionside) receiving the wireless signal. More specifically, the CIR in thepresent specification is a correlation calculation result that is aresult of taking a correlation between the wireless signal transmittedby the transmission side (hereinafter, also referred to as a transmittedsignal) and the wireless signal received by the reception side(hereinafter, also referred to as a received signal) for each delay timethat is an elapsed time after the transmitted signal is transmitted.

The reception side calculates the CIR by taking a sliding correlationbetween the transmitted signal and the received signal. Morespecifically, the reception side calculates a value obtained bycorrelating the received signal with the transmitted signal delayed by acertain delay time as a characteristic (hereinafter, also referred to asa CIR value) in the delay time. The reception side calculates the CIR bycalculating a CIR value for each delay time. That is, the CIR istime-series transition of the CIR values. Here, the CIR value is acomplex number having an I component and a Q component. A sum of squaresof the I component and the Q component of the CIR value may also bereferred to as a power value of the CIR. In a distance measurementtechnique using UWB, the CIR value is also referred to as a delayprofile. In the distance measurement technique using UWB, a sum ofsquares of the I component and the Q component of the CIR value is alsoreferred to as a power delay profile.

Hereinafter, a CIR calculation process in a case where the transmissionside is the portable device 100 and the reception side is the in-vehicledevice 200 will be described in detail with reference to FIGS. 3 and 4 .

FIG. 3 is a diagram illustrating an example of a communicationprocessing block of the communication unit 220 according to the presentembodiment. As shown in FIG. 3 , the communication unit 220 includes anoscillator 222, a multiplier 223, a 90-degree phase shifter 224, amultiplier 225, a low-pass filter (LPF) 226, an LPF 227, a correlator228, and an integrator 229.

The oscillator 222 generates a signal having the same frequency as afrequency of a carrier wave that carries the transmitted signal, andoutputs the generated signal to the multiplier 223 and the 90-degreephase shifter 224.

The multiplier 223 multiplies the received signal received by theantenna 221 by the signal output from the oscillator 222, and outputs aresult of the multiplication to the LPF 226. The LPF 226 outputs asignal having a frequency equal to or lower than the frequency of thecarrier wave carrying the transmitted signal among input signals to thecorrelator 228. The signal input to the correlator 228 is the Icomponent (that is, a real part) of components corresponding to anenvelope of the received signal.

The 90-degree phase shifter 224 delays a phase of the input signal by 90degrees, and outputs the delayed signal to the multiplier 225. Themultiplier 225 multiplies the received signal received by the antenna221 and the signal output from the 90-degree phase shifter 224, andoutputs a result of the multiplication to the LPF 227. The LPF 227outputs a signal having a frequency equal to or lower than the frequencyof the carrier wave carrying the transmitted signal among input signalsto the correlator 228. The signal input to the correlator 228 is the Qcomponent (that is, an imaginary part) of the components correspondingto the envelope of the received signal.

The correlator 228 calculates the CIR by taking a sliding correlationbetween the received signal configured with the I component and the Qcomponent output from the LPF 226 and the LPF 227 and a referencesignal. The reference signal here is the same signal as the transmittedsignal before the carrier wave is multiplied.

The integrator 229 integrates and outputs the CIR output from thecorrelator 228.

The communication unit 220 performs the above process for each of thereceived signals received by the plurality of antennas 221.

FIG. 4 is a graph illustrating an example of the CIR according to thepresent embodiment output from the integrator 229. The horizontal axisof the graph is a delay time, and the vertical axis is a delay profile.One piece of information forming information that changes over time,such as a CIR value in a certain delay time in the CIR, is also called asampling point. In the CIR, typically a set including sampling pointsbetween zero crossing points corresponds to a single pulse. A zerocrossing point is a sampling point where a value becomes zero. However,this is not applied in a noisy environment. For example, a set ofsampling points between intersections of a reference level other thanzero and transition of the CIR value may be regarded as corresponding toone pulse. The CIR shown in FIG. 4 includes a set 21 of sampling pointscorresponding to a certain pulse and a set 22 of sampling pointscorresponding to another pulse.

The set 21 corresponds to, for example, a fast path pulse. A fast pathrefers to the shortest path between transmission and reception, andrefers to a linear distance between transmission and reception in anenvironment in which there is no shield. A fast path pulse is a pulsethat reaches a reception side through a fast path. The set 22corresponds to, for example, a pulse arriving at a reception sidethrough a path other than the fast path.

A pulse detected as a fast path pulse will also be referred to as afirst arrival wave. The first arrival wave may be a direct wave, adelayed wave, or a composite wave. The direct wave is a signal that isdirectly received by a reception side (that is, without being reflectedor the like) via the shortest path between transmission and reception.That is, the direct wave is a fast path pulse. The delayed wave is asignal that is indirectly received by the reception side via anon-shortest path between transmission and reception, that is, reflectedor the like. The delayed wave is received by the reception side with adelay compared with the direct wave. A composite wave is a signalreceived by the reception side in a state in which a plurality ofsignals that have passed through a plurality of different paths arecombined. In the following description, the first arrival wave will besimply referred to as a signal in some cases.

Subsequently, an example of a processing flow related to estimation of apositional relationship between the portable device 100 and thein-vehicle device 200 according to the present embodiment will bedescribed.

2.3. Estimation of Positional Relationship

(1) Distance Estimation

The position estimation unit 325 performs a distance measurementprocess. The distance measurement process is a process of estimating thedistance between the portable device 100 and the in-vehicle device 200.The distance measurement process includes transmitting and receiving adistance measurement signal, and estimating a distance between theportable device 100 and the in-vehicle device 200, that is, a distancemeasurement value, on the basis of the time required for transmittingand receiving the distance measurement signal.

In the distance measurement process, a plurality of distance measurementsignals may be transmitted and received between the portable device 100and the in-vehicle device 200. Among the plurality of distancemeasurement signals, a distance measurement signal transmitted from onedevice to the other device will be referred to as a Poll signal. Adistance measurement signal transmitted as a response to the Poll signalfrom the device that has received the Poll signal to the device that hastransmitted the Poll signal will be referred to as a Resp signal. Adistance measurement signal transmitted as a response to the Resp signalfrom the device that has received the Resp signal to the device that hastransmitted the Resp signal will be referred to as a Final signal.Although the portable device 100 and the in-vehicle device 200 cantransmit and receive any of the distance measurement signals, in thepresent specification, an example in which the portable device 100transmits a Poll signal will be described.

(2) Arrival Angle Estimation

The position estimation unit 325 estimates an arrival angle of a signaltransmitted and received between the devices. In the presentspecification, a Final signal included in the distance measurementsignals will be described as a signal for estimating an arrival angle.

Hereinafter, an example of a process related to distance estimation andarrival angle estimation will be described with reference to FIG. 5 .

FIG. 5 is a sequence diagram for describing an example of a processrelated to positional relationship estimation between devices executedin the system 1 according to the present embodiment.

First, the antenna 121 of the portable device 100 transmits a Pollsignal to the antenna 221A of the in-vehicle device 200 (S101).

Next, the antenna 221A of the in-vehicle device 200 transmits a Respsignal to the antenna 121 of the portable device 100 as a response tothe Poll signal (S103).

The antenna 121 of the portable device 100 transmits a Final signal tothe antenna 221A, the antenna 221B, the antenna 221C, and the antenna221D of the in-vehicle device 200 as a response to the Resp signal(S105).

Here, a time length from the transmission of the Poll signal to thereception of the Resp signal by the portable device 100 is set as a timelength T1, and a time length from the reception of the Resp signal tothe transmission of the Final signal is set as a time length T2. A timelength from the reception of the Poll signal to the transmission of theResp signal by the in-vehicle device 200 is set as a time length T3, anda time length from the transmission of the Resp signal to the receptionof the Final signal is set as a time length T4.

A distance between the portable device 100 and the in-vehicle device 200may be calculated by using each of the above time lengths. For example,the in-vehicle device 200 may receive a signal including informationregarding the time length T1 and the time length T2 from the portabledevice 100. The control device 300 may receive a signal includinginformation regarding the time length T1, the time length T2, the timelength T3, and the time length T4 from the in-vehicle device 200. Theposition estimation unit 325 calculates a signal propagation time ti byusing the time length T1, the time length T2, the time length T3, andthe time length T4. More specifically, the position estimation unit 325may calculate the signal propagation time ti by using the followingEquation 1.

T=(T1×T4−T2×T3)/(T1+T2+T3+T4)  (1)

The position estimation unit 325 may estimate a distance between theportable device 100 and the in-vehicle device 200 by multiplying thecalculated signal propagation time ti by a known signal speed.

An example in which the position estimation unit 325 estimates thedistance between the portable device 100 and the in-vehicle device 200on the basis of a signal transmitted and received between the antenna121 of the portable device 100 and the antenna 221A of the in-vehicledevice 200 has been described, but the in-vehicle device 200 maytransmit and receive a signal by using an antenna different from theantenna 221A, or may transmit and receive a signal by using a pluralityof antennas 221.

The signal propagation time ti is not limited to a calculation methodbased on Equation 1. For example, the signal propagation time may alsobe calculated by subtracting the time length T3 from the time length T1and dividing the time by 2.

Next, an arrival angle of a signal may be calculated from a phasedifference of a Final signal received by an adjacent antenna among theplurality of antennas 221 of the in-vehicle device 200. For example, aphase of the Final signal received by the antenna 221A is set as a phaseP_(A), a phase of the Final signal received by the antenna 221B is setas a phase P_(B), a phase of the Final signal received by the antenna221C is set as a phase P_(C), and a phase of the Final signal receivedby the antenna 221D is set as a phase P_(D).

For example, a coordinate system is defined in which a straight lineconnecting the antenna 221A and the antenna 221B is an X axis, astraight line connecting the antenna 221A and the antenna 221Corthogonal to the X axis is a Y axis, and a vertical direction of theantenna 221A is the Z axis.

In the case of such a coordinate system, each of phase differencesPd_(AB) and Pd_(CD) between the antennas adjacent to each other in theX-axis direction and phase differences Pd_(AC) and Pd_(BD) between theantennas adjacent to each other in the Y-axis direction are expressed byusing the following Equation 2.

Pd _(AB)=(P _(B) −P _(A))

Pd _(CD)=(P _(D) −P _(C))

Pd _(AC)=(P _(C) −P _(A))

Pd _(BD)=(P _(D) −P _(B))  (2)

Here, an angle formed between the straight line connecting the antenna221A and the antenna 221B (or the antenna 221C and the antenna 221D) andthe first arrival wave will be referred to as a formed angle θ. An angleformed between the straight line connecting the antenna 221A and theantenna 221C (or the antenna 221B and the antenna 221D) and the firstarrival wave will be referred to as a formed angle Φ. Here, each of theformed angle θ and the formed angle Φ are arrival angles of a signal,and are expressed by Equation 3. Here, λ is a wavelength of a radio waveand d is a distance between the antennas.

Θ or Φ=arccos(λ×Pd/(2πd))  (3)

Therefore, the position estimation unit 325 calculates an arrival angleof a signal by using Equation 4 on the basis of Equations 2 and 3.

Θ_(AB)=arccos(λ×(P _(B) −P _(A))/(2πd))

Θ_(CD)=arccos(λ×(P _(D) −P _(C))/(2πd))

Φ_(AC)=arccos(λ×(P _(C) −P _(A))/(2πd))

Φ_(BD)=arccos(λ×(P _(D) −P _(B))/(2πd))  (4)

The position estimation unit 325 may calculate the angle θ forming anaverage value of θ_(AB) and θ_(CD), or may estimate the angle θ formingeither θ_(AB) or θ_(CD). Similarly, the position estimation unit 325 maycalculate the angle Φ forming an average value of Φ_(AC) and Φ_(BD), ormay estimate the angle Φ forming either Φ_(AC) or Φ_(BD).

The position estimation unit 325 may estimate a two-dimensional positionor a three-dimensional position of the portable device 100 by using theestimated distance measurement value and the formed angle θ or theformed angle Φ.

For example, in the coordinate system described above, the positionestimation unit 325 may estimate a three-dimensional position of theportable device 100 by using Equation 5.

X=R×cos θ

Y=R×cos Φ

Z=(R2−x2−y2)  (5)

As described above, the position estimation unit 325 may estimate apositional relationship between the portable device 100 and thein-vehicle device 200 on the basis of the signals transmitted andreceived between the plurality of antennas 221 of the in-vehicle device200 and the antennas 121 of the portable device 100. On the other hand,as described above, the estimation accuracy of a positional relationshipmay be reduced depending on the multipath environment generated betweenthe plurality of antennas 221 of the in-vehicle device 200 and theantennas 121 of the portable device 100.

Therefore, on the basis of a signal received by any of the antennas ofthe in-vehicle device 200 or the antenna 121 of the portable device 100,the position estimation unit 325 calculates a reliability parameterindicating the degree of whether or not signals transmitted and receivedbetween the plurality of antennas 221 of the in-vehicle device 200 andthe antenna 121 of the portable device 100 are appropriate as processingtargets for estimating a positional relationship. By using a signal forwhich the reliability parameter satisfies a predetermined criterion forestimating a positional relationship, the position estimation unit 325can estimate a positional relationship between the portable device 100and the in-vehicle device 200 with higher accuracy.

Hereinafter, a specific example of the reliability parameter calculatedby the parameter calculation unit 321 will be described.

2.4. Reliability Parameter

The parameter calculation unit 321 according to the present embodimentcalculates a reliability parameter on the basis of a signal received bythe communication unit 220. Here, the received signal may be the abovePoll signal, Resp signal, or Final signal, or may be a signaltransmitted separately from the distance measurement signal from theportable device 100.

The reliability parameter is an index indicating the degree of whetheror not a signal received by the antenna 121 of the communication unit120 or any of the antennas 221 of the communication unit 220 isappropriate as a processing target for estimating a positionalrelationship between the portable device 100 and the in-vehicle device200. For example, the reliability parameter is a continuous value or adiscrete value, and as a value thereof increases, a signal transmittedand received by the antennas may become more appropriate as a processingtarget for estimating a positional relationship, and as the valuedecreases, the signal may become more inappropriate as a processingtarget for estimating a positional relationship. As a value of thereliability parameter increases, a signal transmitted and received bythe antennas may become more inappropriate as a processing target forestimating a positional relationship, and as the value decreases, andthe signal may become more appropriate as a processing target forestimating a positional relationship. Hereinafter, a reliabilityparameter based on a signal received by the communication unit 220 willbe described with reference to specific examples.

Index Indicating Magnitude of Noise

The reliability parameter may be, for example, an index indicating amagnitude of noise. More specifically, the parameter calculation unit321 may calculate the reliability parameter on the basis of at least oneof a power value and a signal noise ratio (SNR) of a signal received bythe communication unit 220. Since the influence of noise is small in acase where the power value or the SNR is large, a first reliabilityparameter indicating that the first arrival wave is appropriate as adetection target is calculated. On the other hand, since the influenceof noise is large in a case where the power value or the SNR is small, areliability parameter indicating that the first arrival wave isinappropriate as a detection target may be calculated.

Index Indicating Validity that First Arrival Wave is Based on DirectWave

The reliability parameter is an index indicating the validity that thefirst arrival wave is based on a direct wave. The higher the validitythat the first arrival wave is based on a direct wave, the higher thereliability, and the lower the validity that the first arrival wave isbased on a direct wave, the lower the reliability.

For example, the reliability parameter may be calculated on the basis ofthe consistency between signals in each of the plurality of antennas 221of the communication unit 220. More specifically, the parametercalculation unit 321 may calculate a reliability parameter on the basisof at least one of a signal reception time and a power value in each ofthe plurality of antennas 221 of the communication unit 220. Due to theinfluence of multipath, a plurality of signals arriving via differentpaths may be combined and received by the antennas in a state of beingamplified or canceled out by each other. In a case where the way ofamplifying and canceling out of a signal is different in each of theplurality of antennas, the reception time and the power value of thesignal may be different among the plurality of antennas. Consideringthat a distance between the antennas is a short distance of about ½ of awavelength of a signal for estimating an arrival angle, a largedifference in a signal reception time and a power value between theantenna 221A, the antenna 221B, the antenna 221C, and the antenna 221Dmeans that the validity that the signal is based on a direct wavebecomes lower.

Therefore, a reliability parameter indicating that the validity that thefirst arrival wave is based on a direct wave becomes lower as adifference in the reception time of the first arrival wave (that is, adelay time of a specific element) between the plurality of antennas 221becomes larger is calculated. On the other hand, a reliability parameterindicating that the validity that the first arrival wave is based on adirect wave becomes higher as a difference in the reception time of thefirst arrival wave between the plurality of antennas 221 becomes smalleris calculated. A reliability parameter indicating that the validity thatthe first arrival wave is based on a direct wave becomes lower as adifference in the power of the first arrival wave between the pluralityof antennas 221 becomes larger is calculated. On the other hand, areliability parameter indicating that the validity that the firstarrival wave is based on a direct wave becomes higher as a difference inthe power of the first arrival wave between the plurality of antennas221 becomes smaller is calculated.

The reliability parameter may be calculated on the basis of theconsistency between position parameters indicating a position where theportable device 100 is present and estimated on the basis of the firstarrival wave received by each of a plurality of antenna pairs formed bytwo different antennas (for example, the antenna 221A and the antenna221B) among the plurality of antennas 221. The position parameters hereare the distance measurement value, the formed angles θ and Φ, and thecoordinates (x,y,z). In a case where the first arrival wave is based ona direct wave, results of the formed angles θ and Φ and the coordinates(x,y,z) are the same or substantially the same even if combinations ofantenna pairs of the communication unit 220 used for calculating theformed angles θ and Φ and the coordinates (x,y,z) are different.However, in a case where the first arrival wave is not based on a directwave, there may be differences in results of the formed angles θ and Φand the coordinates (x,y,z) in different antenna pairs of thecommunication unit 220.

Therefore, a reliability parameter indicating that the validity that thefirst arrival wave is based on a direct wave becomes higher as adifference in a calculation result of a position parameter betweencombinations of different antenna pairs becomes smaller is calculated.For example, a reliability parameter indicating that the validity thatthe first arrival wave is based on a direct wave becomes higher as anerror between Φ_(AC) and Φ_(BD) and an error between θ_(AB) and θ_(CD)described in the angle estimation process are reduced is calculated. Onthe other hand, a reliability parameter indicating that the validitythat the first arrival wave is based on a direct wave becomes lower as adifference in a calculation result of a position parameter betweencombinations of different antenna pairs becomes larger is calculated.For example, a reliability parameter indicating that the validity thatthe first arrival wave is based on a direct wave becomes lower as anerror between Φ_(AC) and Φ_(BD) and an error between θ_(AB) and θ_(CD)described in the angle estimation process are increased is calculated.However, a reliability parameter calculated by using differences in theformed angles θ and Φ and the coordinates (x,y,z) is a reliabilityparameter for the entire antenna, and thus is not applied in Example 1that will be described later.

Index indicating validity that first arrival wave is not based oncomposite wave

The reliability parameter may be an index indicating the validity thatthe first arrival wave is not based on a composite wave. The higher thevalidity that the first arrival wave is not based on a composite wave,the higher the reliability, and the lower the validity that the firstarrival wave is not based on a composite wave, the lower thereliability. Specifically, the reliability parameter may be calculatedon the basis of at least one of a width of the first arrival wave in thetime direction and a phase state in the first arrival wave.

Index indicating validity of situation in which wireless signal isreceived The reliability parameter may be an index indicating thevalidity of a situation in which a wireless signal is received. Thehigher the validity of a situation in which a wireless signal isreceived, the higher the reliability, and the lower the validity of thesituation in which the wireless signal is received, the lower thereliability.

For example, the reliability parameter may be calculated on the basis ofa variation of a plurality of first arrival waves. In this case, thereliability parameter may be calculated on the basis of a statisticindicating a variation of a plurality of first arrival waves, such as avariance of power values of the first arrival waves, and variances andamounts of change of the estimated position parameters (the distance,the formed angles θ and Φ, and the coordinates (x,y,z)).

Difference Between Delay Time of First Element and Delay Time of SecondElement

The reliability parameter may be a difference between a delay time of afirst element in which a CIR value peaks first after a specific elementin CIR and a delay time of a second element in which the CIR value peakssecond after the specific element. As shown in FIG. 4 , a CIR waveformof the first arrival wave is a waveform having one peak. On the otherhand, when a composite wave is detected as the first arrival wave, a CIRwaveform of the first arrival wave may be a waveform including aplurality of peaks. Whether the CIR waveform of the first arrival wavehas one peak or a plurality of peaks may be determined on the basis of adifference between the delay time of the first element and the delaytime of the second element.

In a case where a composite wave is detected as the first arrival wave,the estimation accuracy of a position parameter is lower than in a casewhere a direct wave is detected as the first arrival wave. Therefore, itcan be said that the larger the difference between the delay time of thefirst element and the delay time of the second element, the higher thereliability.

Correlation of CIR Waveform

The reliability parameter may be derived on the basis of a correlationof a CIR waveform in a certain antenna pair among the plurality ofantennas 221 of the communication unit 220. In a case where a directwave and a delayed wave are received in a combined state in theplurality of antennas 221 of the communication unit 220, a phaserelationship between the direct wave and the delayed wave may bedifferent between antennas even if the distance between the antennas isshort. As a result, CIR waveforms in the respective antennas may bedifferent. That is, the fact that the CIR waveforms differ in a certainantenna pair means that a composite wave is received in at least one ofthe antenna pairs. In a case where a composite wave is detected as thefirst arrival wave, that is, in a case where a specific elementcorresponding to a direct wave is not detected, the estimation accuracyof a position parameter is reduced.

For example, the reliability parameter may be a correlation coefficientbetween a CIR obtained on the basis of a received signal received fromone antenna and a CIR obtained on the basis of a received signalreceived by another antenna among the plurality of antennas 221 of thecommunication unit 220. In this case, the reliability parameter isdetermined to be less reliable as the correlation coefficient becomessmaller, and is determined to be more reliable as the correlationcoefficient becomes larger. The correlation coefficient includes, forexample, a Pearson's correlation coefficient.

Supplement

Hereinafter, a supplement relating to a specific example of thereliability parameter described below will be described.

First, each of a plurality of sampling points included in a CIR willalso be referred to as an element below. That is, the CIR includes a CIRvalue for each delay time as an element. A shape of the CIR, morespecifically, a shape of a time-series change of the CIR value will alsobe referred to as a CIR waveform.

Among a plurality of elements included in the CIR, a specific elementwill also be referred to as a specific element below. The specificelement is an element corresponding to the first arrival wave. Thespecific element is detected according to the predetermined detectioncriterion described above for the first arrival wave. As an example, thespecific element is an element of which an amplitude or power as a CIRvalue first exceeds a predetermined threshold value among a plurality ofelements included in the CIR. Hereinafter, such a predeterminedthreshold value will also be referred to as a fast path threshold value.

The time corresponding to a delay time of the specific element is usedfor measuring a distance as a reception time of the first arrival wave.A phase of the specific element is used for estimating an arrival angleof a signal as a phase of the first arrival wave.

The plurality of antennas 221 of the communication unit 220 may includethe communication unit 220 in a line of sight (LOS) state and thecommunication unit 220 in a non-line of sight (NLOS) state.

The LOS state means that a space between the antenna 221 of thein-vehicle device 200 and the antenna 121 of the portable device 100 canbe seen. In the LOS state, the reception power of a direct wave is thelargest, and thus a reception side is likely to succeed in detecting thedirect wave as the first arrival wave.

The NLOS state means that the antenna 221 of the in-vehicle device 200and the antenna 121 of the portable device 100 cannot be seen. In theNLOS state, the reception power of a direct wave may be smaller than theothers, and thus a reception side may fail to detect the direct wave asthe first arrival wave.

In a case where the communication unit 220 is in the NLOS state, thereception power of a direct wave among signals arriving from theportable device 100 becomes smaller than that of noise. Therefore, evenif the direct wave is successfully detected as the first arrival wave, Aphase and reception time of the first arrival wave may vary due to theinfluence of noise. In that case, the distance measurement accuracy andthe arrival angle estimation accuracy may decrease.

In a case where the communication unit 220 is in the NLOS state, thereception power of a direct wave is smaller than in a case where thecommunication unit 220 is in the LOS state, and it may fail to detectthe direct wave as the first arrival wave. In that case, the distancemeasurement accuracy and the arrival angle estimation accuracy maydecrease.

Difference Between Delay Time of Specific Element and Delay Time ofElement Having Maximum CIR Value

Therefore, the reliability parameter may be a difference between a delaytime of the specific element and a delay time of an element having themaximum CIR value in the CIR.

If the communication unit 220 is in the LOS state, a CIR value of adirect wave is the largest. Therefore, an element having the maximum CIRvalue in the CIR is included in a set corresponding to the direct wave.

On the other hand, in the NLOS state, a CIR value of a delayed wave maybe greater than a CIR value of a direct wave. This is because in theNLOS state, there is a shield in the middle of the fast path. Inparticular, if there is a human body in the middle of the fast path, adirect wave is greatly attenuated when the direct wave passes throughthe human body. In that case, an element having the maximum CIR value inthe CIR is not included in the set corresponding to the direct wave.

Whether the communication unit 220 is in the LOS state or the NLOS statemay be determined on the basis of a difference between the delay time ofthe specific element and the delay time of the element having themaximum CIR value in the CIR.

This is because the difference may be small in a case where thecommunication unit 220 is in the LOS state. This is because thedifference may be large in a case where the communication unit 220 is inthe NLOS state.

The specific example of the reliability parameter according to thepresent embodiment has been described above. The position estimationunit 325 can improve the estimation accuracy of a positionalrelationship between the portable device 100 and the in-vehicle device200 by using a reliability parameter calculated by the parametercalculation unit 321.

The position estimation unit 325 may use a distance measurement value asa reliability parameter in addition to the above reliability parameter,or may use a plurality of reliability parameters in combination.Hereinafter, specific examples using a reliability parameter will besequentially described.

3. Examples 3.1. Example 1

The control unit 320 related to Example 1 may perform control forestimating a positional relationship between the portable device 100 andthe in-vehicle device 200 by applying a weight parameter based on areliability parameter calculated on the basis of a signal received fromthe portable device 100 by the in-vehicle device 200 to a phasedifference between adjacent antennas of the plurality of antennas 221 ofthe in-vehicle device 200.

Here, the adjacent antennas refer to the antenna 221A and the antenna221B, the antenna 221C and the antenna 221D, the antenna 221A and theantenna 221C, and the antenna 221B and the antenna 221D, shown in FIG. 2.

The control unit 320 may perform weighted averaging based on a weightparameter on a phase difference between antennas in directions parallelto each other among the plurality of antennas 221 and perform controlfor estimating a positional relationship between the portable device 100and the in-vehicle device 200. The antennas in the parallel directionare an antenna pair including the antenna 221A and the antenna 221Bparallel to the X-axis described above, and an antenna pair includingthe antenna 221C and the antenna 221D. The antennas in the paralleldirection are an antenna pair including the antenna 221A and the antenna221C parallel to the Y axis described above, and an antenna pairincluding the antenna 221B and the antenna 221D.

For example, a phase difference between antennas after weightedaveraging for each antenna pair parallel to the X axis is set as aninter-antenna phase difference Pd_(X), and a phase difference betweenantennas after weighted averaging for each antenna pair parallel to theY axis is set as an inter-antenna phase difference Pd_(Y). A weightparameter for an inter-antenna phase difference Pd_(AB) of the antenna221A and the antenna 221B is set as a weight parameter W_(AB), a weightparameter for an inter-antenna phase difference Pd_(CD) of the antenna221C and the antenna 221D is set as a weight parameter W_(CD), a weightparameter for an inter-antenna phase difference Pd_(AC) of the antenna221A and the antenna 221C is set as a weight parameter WAC, and a weightparameter for an inter-antenna phase difference Pd_(BD) of the antenna221B and the antenna 221D is set as a weight parameter W_(BD).

Here, the parameter calculation unit 321 may set, for example, valuesindicated by reliability parameters as the weight parameters W_(AB),W_(CD), W_(AC), and W_(BD). For example, in a case where the reliabilityparameter is the above reception power, when the reception power of asignal received by the antenna 221A is “−90 dBm” and the reception powerof a signal received by the antenna 221B is “−100 dBm”, the weightparameter W_(AB) may be “−95 dBm” which is an average value of “−90 dBm”and “−100 dBm”. Alternatively, the weight parameter W_(AB) may be “−90dBm”, which is the maximum value of “−90 dBm” and “−100 dBm”, or “−100dBm”, which is the minimum value. Alternatively, the weight parameterW_(AB) may be a median value of the reception power of the plurality ofantennas 221.

The position estimation unit 325 may estimate the inter-antenna phasedifference Pd_(X) in the X-axis direction and the inter-antenna phasedifference Pd_(Y) in the Y-axis direction by using Equation 6.

Pd _(X)=(W _(AB) ×Pd _(AB) +W _(CD) ×Pd _(CD))/(W _(AB) +W _(CD))

Pd _(Y)=(W _(AC) ×Pd _(AC) +W _(BD) ×Pd _(BD))/(W _(AC) +W _(BD))  (6)

The position estimation unit 325 calculates the formed angle θ on thebasis of the Pd_(X) estimated by using Equation 6 and Equation 3, andcalculates the formed angle Φ on the basis of Pd_(Y) estimated by usingEquation 6 and Equation 3. As a result, the position estimation unit 325can estimate a positional relationship between the portable device 100and the in-vehicle device 200 with higher accuracy.

In the example described above, an example in which the parametercalculation unit 321 sets a value indicated by a reliability parameteras a weight parameter has been described, but a weight parameter is notlimited to the above example. Hereinafter, another example of a methodof calculating a weight parameter in the parameter calculation unit 321will be described with reference to FIGS. 6A to 7D. First, withreference to FIGS. 6A to 6D, a specific example of a method ofcalculating a weight parameter in a case where the reliability becomeshigher as a value of the reliability parameter becomes smaller will bedescribed. In the following description, a method of calculating aweight parameter on the basis of a reliability parameter of the antennapair of the antenna 221A and the antenna 221B will be described.

FIG. 6A is an explanatory diagram for describing an example of a methodof calculating a weight parameter according to a first specified value.The parameter calculation unit 321 may calculate a weight parameter Wonthe basis of, for example, a reliability parameter Rp and Equation 7.

W=1(Rp<TH)

W=0(Rp≥TH)  (7)

For example, the parameter calculation unit 321 may calculate a firstvalue when the reliability parameter Rp_(AB) is equal to or more thanthe specified value TH, and calculate a second value when thereliability parameter Rp_(AB) is less than the specified value TH.

The first value may be, for example, “0” as shown in FIG. 6A. The secondvalue may be, for example, “1” as shown in FIG. 6A. However, the firstvalue and the second value may be any values as long as the first valueis smaller than the second value. Consequently, the parametercalculation unit 321 can set a weight parameter according to a simplercalculation method.

The parameter calculation unit 321 may calculate the first value whenthe reliability parameter Rp is equal to or more than a first specifiedvalue, and calculate the second value when the reliability parameter Rpis less than a second specified value smaller than the first specifiedvalue. The parameter calculation unit 321 may calculate a third value byusing a specified function when the reliability parameter Rp is equal toor more than the second specified value and less than the firstspecified value. Here, the specified function may be, for example, amonotonic increase or monotonic decrease function. In this case, whenthe smaller the reliability parameter, the higher the reliability, thespecified function is a monotonic decrease function, and when the largerthe reliability parameter, the higher the reliability, the specifiedfunction is a monotonic increase function. First, with reference toFIGS. 6B to 6D, a specific example of a method of calculating a weightparameter when the specified function is a monotonic decrease functionwill be described.

FIG. 6B is an explanatory diagram for describing an example of a weightparameter calculation method using a linear function as a specifiedfunction. The parameter calculation unit 321 may calculate the weightparameter W on the basis of the reliability parameter Rp and Equation 8.

W=1(Rp<TH2)

W=−(Rp _(AB) −TH2)/(TH1−TH2)+1(TH2≤Rp<TH1)

W=0(Rp≥TH1)  (8)

The parameter calculation unit 321 calculates “0” as the first valuewhen the reliability parameter Rp_(AB) is equal to or more than thefirst specified value TH1, and calculates “1” as the second value whenthe reliability parameter Rp_(AB) is less than the second specifiedvalue. The parameter calculation unit 321 may calculate the third valueby using a linear function as the specified function when thereliability parameter Rp_(AB) is equal to or more than the secondspecified value TH2 and less than the first specified value TH1.

FIG. 6C is an explanatory diagram for describing an example of a weightparameter calculation method using a trigonometric function as aspecified function. The parameter calculation unit 321 may calculate theweight parameter Won the basis of the reliability parameter Rp andEquation 9.

W=1(Rp<TH2)

W=cos[(Rp _(AB) −TH2)/(TH1−TH2)×π/2](TH2≤Rp<TH1)

W=0(Rp≥TH1)  (9)

The parameter calculation unit 321 calculates “0” as the first valuewhen the reliability parameter Rp_(AB) is equal to or more than thefirst specified value TH1, and calculates “1” as the second value whenthe reliability parameter Rp_(AB) is less than the second specifiedvalue. The parameter calculation unit 321 may calculate the third valueby using a trigonometric function as the specified function when thereliability parameter Rp_(AB) is equal to or more than the secondspecified value TH2 and less than the first specified value TH1.

FIG. 6D is an explanatory diagram for describing an example of a weightparameter calculation method using an exponential function as aspecified function. The parameter calculation unit 321 may calculate theweight parameter Won the basis of the reliability parameter Rp andEquation 10.

W=1(Rp<TH2)

W=exp[−5×(Rp _(AB) −TH2)/(TH1−TH2)](TH2≤Rp<TH1)

W=0(Rp≥TH1)  (10)

The parameter calculation unit 321 calculates “0” as the first valuewhen the reliability parameter Rp_(AB) is equal to or more than thefirst specified value TH1, and calculates “1” as the second value whenthe reliability parameter Rp_(AB) is less than the second specifiedvalue. The parameter calculation unit 321 may calculate the third valueby using an exponential function as the specified function when thereliability parameter Rp_(AB) is equal to or more than the secondspecified value TH2 and less than the first specified value TH1.

The specific example of the weight parameter calculation method in thecase where the reliability becomes higher as the reliability parameterRp becomes smaller has been described above. Subsequently, withreference to FIG. 7 , a specific example of a method for calculating aweight parameter in a case where the reliability becomes higher as thereliability parameter Rp becomes larger will be described.

FIG. 7A is an explanatory diagram for describing an example of a methodof calculating a weight parameter according to the first specifiedvalue. The parameter calculation unit 321 may calculate the weightparameter W on the basis of the reliability parameter Rp and Equation11.

W=0(Rp<TH)

W=1(Rp≥TH)  (11)

Similar to Equation 7, the parameter calculation unit 321 may calculatea first value when the reliability parameter Rp_(AB) is equal to or morethan the specified value TH, and calculate a second value when thereliability parameter Rp_(AB) is less than the specified value TH.

In Equation 7, the first value may be any value as long as the firstvalue is smaller than the second value, but in Equation 11, the firstvalue is any value as long as the first value is greater than the secondvalue. The first value may be, for example, “1” as shown in FIG. 7A. Thesecond value may be, for example, “0” as shown in FIG. 7A.

That is, in a case where the reliability becomes higher as thereliability parameter becomes larger, the magnitude relationship betweenthe first value and the second value described in the case where thereliability becomes higher as the reliability parameter becomes smalleris exchanged. A specific example of a method of calculating a weightparameter when the specified function is a monotonic increase functionwill be described with reference to FIGS. 7B to 7D below, and repeateddescription of FIGS. 6B to 6D will be omitted.

FIG. 7B is an explanatory diagram for describing an example of a weightparameter calculation method using a linear function as a specifiedfunction. The parameter calculation unit 321 may calculate the weightparameter W on the basis of the reliability parameter Rp and Equation12.

W=0(Rp<TH2)

W=−(Rp _(AB) −TH2)/(TH1−TH2)+1(TH2≤Rp<TH1)

W=1(Rp≥TH1)  (12)

FIG. 7C is an explanatory diagram for describing an example of a weightparameter calculation method using a trigonometric function as aspecified function. The parameter calculation unit 321 may calculate theweight parameter Won the basis of the reliability parameter Rp andEquation 13.

W=0(Rp<TH2)

W=sin[(Rp _(AB) −TH2)/(TH1−TH2)×π/2](TH2≤Rp<TH1)

W=1(Rp≥TH1)  (13)

FIG. 7D is an explanatory diagram for describing an example of a weightparameter calculation method using an exponential function as aspecified function. The parameter calculation unit 321 may calculate theweight parameter Won the basis of the reliability parameter Rp andEquation 14.

W=0(Rp<TH2)

W=exp[5×(Rp _(AB) −TH2)/(TH1−TH2)−1](TH2≤Rp<TH1)

W=1(Rp≥TH1)  (14)

The parameter calculation unit 321 calculates a weight parameter byusing at least one of the specific examples related to the weightparameter calculation method for each antenna pair. The positionestimation unit 325 calculates the inter-antenna phase difference Pd_(X)in the X-axis direction and the inter-antenna phase difference Pd_(Y) inthe Y-axis direction on the basis of the calculated weight parameter andEquation 6. The position estimation unit 325 calculates the formed angleθ and the formed angle Φ of a signal as arrival angles of the signal onthe basis of each of the inter-antenna phase differences Pd_(X) andPd_(Y) calculated by applying the weight parameter and Equation 3.Consequently, the position estimation unit 325 can reduce the influenceof the multipath environment and calculate the arrival angle of thesignal with higher accuracy.

Example of Operation Process

FIG. 8 is an explanatory diagram for describing an example of anoperation process of the system 1 related to Example 1. First, thecommunication unit 120 included in the portable device 100 transmits aPoll signal, and the communication unit 220 included in the in-vehicledevice 200 receives the Poll signal (S201).

Subsequently, the communication unit 220 transmits a Resp signal as aresponse to the Poll signal, and the communication unit 120 receives theResp signal (S203).

The communication unit 120 transmits a Final signal as a response to theResp signal, and the communication unit 220 receives the Final signal(S205). Here, the communication unit 220 transmits various types ofinformation regarding the signals transmitted and received to and fromthe communication unit 120 to the communication unit 310 included in thecontrol device 300.

Subsequently, the position estimation unit 325 calculates ae distancemeasurement value on the basis of the signals transmitted and receivedbetween the portable device 100 and the in-vehicle device (S207).

Subsequently, the parameter calculation unit 321 calculates areliability parameter on the basis of the signals received by thein-vehicle device 200 (S209).

The parameter calculation unit 321 calculates a weight parameter on thebasis of the calculated reliability parameter (S211).

The position estimation unit 325 performs weighted averaging on each ofinter-antenna phase differences by using the weight parameter calculatedby the parameter calculation unit 321 (S213).

Subsequently, the position estimation unit 325 estimates an arrivalangle of the signal received from the portable device 100 by using theinter-antenna phase difference subjected to the weighted averaging(S215).

The position estimation unit 325 calculates a three-dimensional positionof the portable device 100 on the basis of the estimated arrival angleof the signal and the distance measurement value (S217).

The control unit 320 determines whether or not the three-dimensionalposition of the portable device 100 calculated by the positionestimation unit 325 satisfies a predetermined criterion (S219). In acase where the predetermined criterion is satisfied (S219: Yes), thecontrol unit 320 causes the process to proceed to S221, and in a casewhere the predetermined criterion is not satisfied (S219: No), thecontrol unit 320 ends the process.

In a case where a predetermined criterion is satisfied (S219: Yes), thecontrol unit 320 performs operation control related to starting orstopping an engine, which is an example of the operation device 400(S221), and the control unit 320 ends the process.

The control example related to Example 1 has been described above.According to the control related to Example 1, the control device 300makes it possible to reduce the influence of the multipath, and canestimate a positional relationship between the portable device 100 andthe in-vehicle device 200 with higher accuracy. Subsequently, Example 2will be described with reference to FIGS. 9 to 11 .

3.2. Example 2

The control unit 320 related to Example 2 performs control forestimating a positional relationship between the portable device 100 andthe in-vehicle device 200 by applying a weight parameter based on areliability parameter calculated on the basis of a signal received bythe in-vehicle device 200 from the portable device 100 to at least twoprovisional positional relationships estimated on the basis of signalstransmitted and received between the in-vehicle device 200 and theportable device 100.

For example, the position estimation unit 325 related to Example 2estimates a provisional positional relationship between the portabledevice 100 and the in-vehicle device 200 on the basis of signalstransmitted and received by each of the antenna 221A, the antenna 221B,and the antenna 221C, and the portable device 100 as shown in FIG. 2 .The position estimation unit 325 related to Example 2 estimates aprovisional positional relationship between the portable device 100 andthe in-vehicle device 200 on the basis of signals transmitted andreceived by each of the antenna 221A, the antenna 221C, and the antenna221D, and the portable device 100 as shown in FIG. 2 . The positionestimation unit 325 related to Example 2 estimates a provisionalpositional relationship between the portable device 100 and thein-vehicle device 200 on the basis of signals transmitted and receivedby each of the antenna 221B, the antenna 221C, and the antenna 221D, andthe portable device 100 as shown in FIG. 2 .

The parameter calculation unit 321 calculates a reliability parameterbased on a signal received by the portable device 100 for each antennaor antenna pair of the in-vehicle device 200. The parameter calculationunit 321 calculates a weight parameter on the basis of a calculatedreliability parameter by using any of the methods described in Example1.

In a case where three provisional positional relationships are estimatedas described above, the position estimation unit 325 related to Example2 may apply the above weight parameter to the three provisionalpositional relationships, to estimate a positional relationship betweenthe portable device 100 and the in-vehicle device 200.

Although the case where three provisional positional relationships areestimated has been described, any number of provisional positionalrelationships may be estimated as long as at least two provisionalpositional relationships are estimated. As long as the number ofantennas included in the in-vehicle device 200 is at least three, amethod of estimating a positional relationship between the portabledevice 100 and the in-vehicle device 200 related to Example 2 can beapplied.

Example 1, Example 2, and Example 3 are also applicable in a case wherea plurality of in-vehicle devices 200 are mounted on the vehicle 20.Hereinafter, a case where two in-vehicle devices 200 are mounted on thevehicle 20 related to Example 2 and Example 3 will be described.

FIG. 9 is a block diagram illustrating a configuration example of thevehicle 20 related to Example 2 and Example 3. As shown in FIG. 9 , thevehicle 20 is equipped with an in-vehicle device 200-1 and an in-vehicledevice 200-2. The vehicle 20 may be equipped with three or morein-vehicle devices 200. Since functional configuration examples of thein-vehicle device 200, the control device 300, and the operation device400 are the same as those described with reference to FIG. 1 , thedescription thereof will be omitted.

The control unit 320 related to Example 2 may perform control forestimating a positional relationship between the portable device 100 andthe in-vehicle device 200 by applying a weight parameter based on areliability parameter calculated on the basis of a signal received fromthe portable device 100 by each of the plurality of in-vehicle devices200 to a provisional positional relationship between the portable device100 and the in-vehicle device 200 estimated on the basis of a signaltransmitted and received between each of the plurality of in-vehicledevices 200 and the portable device 100.

First, signals are transmitted and received between the portable device100 and the in-vehicle device 200-1 and the in-vehicle device 200-2, andthe control device 300 acquires information regarding the signalstransmitted and received from the in-vehicle device 200-1 and thein-vehicle device 200-2.

The parameter calculation unit 321 calculates a reliability parameter onthe basis of the signal received from the portable device 100 by thein-vehicle device 200-1. The parameter calculation unit 321 calculates aweight parameter on the basis of the calculated reliability parameter byusing any of the methods described in Example 1.

The parameter calculation unit 321 calculates a reliability parameter onthe basis of the signal received from the portable device 100 by thein-vehicle device 200-2. The parameter calculation unit 321 calculatesthe weight parameter on the basis of the calculated reliabilityparameter by using any of the methods described in Example 1.

Subsequently, the position estimation unit 325 estimates an arrivalangle of the signal and a three-dimensional position of the portabledevice 100 on the basis of the signal transmitted and received betweenthe portable device 100 and the in-vehicle device 200-1. The positionestimation unit 325 estimates an arrival angle of the signal and athree-dimensional position of the portable device 100 on the basis ofthe signal transmitted and received between the portable device 100 andthe in-vehicle device 200-2. The signal arrival angle or thethree-dimensional position of the portable device 100 estimated for eachin-vehicle device 200 is a specific example of a provisional positionalrelationship between the portable device 100 and the in-vehicle device200.

The position estimation unit 325 estimates a positional relationshipbetween the portable device 100 and the in-vehicle device 200 byapplying the weight parameter calculated by the parameter calculationunit 321 to the estimated provisional positional relationship betweenthe portable device 100 and the in-vehicle device 200. Hereinafter, aspecific example of Example 2 will be described with reference to FIG.10 .

FIG. 10 is an explanatory diagram for describing a control example ofthe system 1 related to Example 2. As shown in FIG. 10 , thecommunication unit 220-1 included in the in-vehicle device 200-1 has anantenna 221A-1, an antenna 221B-1, an antenna 221C-1, and an antenna221D-1. The communication unit 220-2 included in the in-vehicle device200-2 has an antenna 221A-2, an antenna 221B-2, an antenna 221C-2, andan antenna 221D-2.

In a case where the reception power is used as a reliability parameter,it is assumed that the parameter calculation unit 321 calculates each ofthe reliability parameters of the antenna 221A-1, the antenna 221B-1,and the antenna 221C-1 as “−90 dBm”, and calculates the reliabilityparameter of the antenna 221D-1 as “−105 dBm”, for example, as shown inFIG. 10 . Subsequently, it is assumed that the parameter calculationunit 321 calculates the reliability parameter of the antenna 221A-2 as“−105 dBm”, and calculates the reliability parameters of the antenna221B-2, the antenna 221C-2, and the antenna 221D-2 as “−90 dBm”.

In this case, the position estimation unit 325 may estimate a positionalrelationship between the portable device 100 and the in-vehicle device200 on the basis of, for example, signals transmitted and received bythree more reliable antennas. For example, the position estimation unit325 may select three antennas 221 in descending order of reliability(for example, the reception power is large), and estimate a provisionalpositional relationship on the basis of the signals transmitted andreceived by the selected antenna 221.

For example, in the example shown in FIG. 10 , three highly reliableantennas are the antenna 221A-1, the antenna 221B-1 and the antenna221C-1 of the communication unit 220-1, and the antenna 221B-2, theantenna 221C-2, and the antenna 221D-2 of the communication unit 220-2.

The position estimation unit 325 estimates a provisional positionalrelationship on the basis of, for example, signals transmitted andreceived by the antenna 221A-1, the antenna 221B-1, and the antenna221C-1 and the antenna 121 of the portable device 100. The positionestimation unit 325 estimates a provisional positional relationship onthe basis of signals transmitted and received by the antenna 221B-2, theantenna 221C-2, the antenna 221D-2, and the antenna 121 of the portabledevice 100.

The position estimation unit 325 applies the weight parameter to eachestimated provisional positional relationship, and estimates apositional relationship between the portable device 100 and thein-vehicle device 200. For example, in a case where the positionalrelationship between the portable device 100 and the in-vehicle device200 is set as a three-dimensional position of the portable device 100with respect to the in-vehicle device 200, the position estimation unit325 uses Equation 15 and performs weighted averaging on the provisionalthree-dimensional position of the portable device 100 to estimate athree-dimensional position of the portable device 100. Here, aprovisional three-dimensional position of the portable device 100estimated on the basis of the signals transmitted and received by theportable device 100 and the in-vehicle device 200-1 is denoted by(x1,y1,z1), and a provisional three-dimensional position of the portabledevice 100 estimated on the basis of the signals transmitted andreceived by the portable device 100 and the in-vehicle device 200-2 isdenoted by (x2,y2,z2). The average reception power of the in-vehicledevice 200-1 is denoted by P1, and the average reception power of thein-vehicle device 200-2 is denoted by P2.

X=(P1×x1+P2×x2)/(P1+P2)

Y=(P1×y1+P2×y2)/(P1+P2)

Z=(P1×z1+P2×z2)/(P1+P2)  (15)

Equation 15 is an example of calculating a weighted average when anaverage value of the reliability parameters (average reception powers P1and P2) is applied as the weight parameter. As the weight parameter, aweight parameter based on a reliability parameter may be calculated byusing each equation described in Example 1.

Example of Operation Process

FIG. 11 is an explanatory diagram for describing an example of anoperation process of the system 1 related to Example 2. First, thecommunication unit 120 included in the portable device 100 transmits aPoll signal, and the communication unit 220-1 included in the in-vehicledevice 200-1 and the communication unit 220-2 included in the in-vehicledevice 200-2 receive the Poll signal (S301).

Subsequently, the communication unit 220-1 and the communication unit220-2 transmit a Resp signal as a response to the Poll signal, and thecommunication unit 120 receives the Resp signal (S303).

The communication unit 120 transmits a Final signal as a response to theResp signal, and the communication unit 220-1 and the communication unit220-2 receive the Final signal (S305). Here, the communication unit220-1 and the communication unit 220-2 transmit various types ofinformation regarding the transmitted and received signals to thecommunication unit 310 included in the control device 300.

Subsequently, the position estimation unit 325 calculates a firstdistance measurement value on the basis of the signals transmitted andreceived between the portable device 100 and the in-vehicle device200-1, and calculates a second distance measurement value on the basisof the signals transmitted and received between the portable device 100and the in-vehicle device 200-2 (S307).

Subsequently, the parameter calculation unit 321 calculates a firstreliability parameter on the basis of the signal received by thein-vehicle device 200-1, and calculates a second reliability parameteron the basis of the signal received by the in-vehicle device 200-2(S309).

The parameter calculation unit 321 calculates a weight parameter on thebasis of each of the calculated reliability parameters (S311). Forexample, the parameter calculation unit 321 calculates a first weightparameter on the basis of the first reliability parameter, andcalculates a second weight parameter on the basis of the secondreliability parameter.

The position estimation unit 325 estimates an arrival angle of a firstsignal on the basis of the signals transmitted and received between theportable device 100 and the in-vehicle device 200-1, and estimates anarrival angle of a second signal on the basis of the signals transmittedand received between the portable device 100 and the in-vehicle device200-2 (S313).

Subsequently, the position estimation unit 325 estimates a firstprovisional three-dimensional position of the portable device 100 on thebasis of the arrival angle of the first signal, and estimates a secondprovisional three-dimensional position of the portable device 100 on thebasis of the arrival angle of the second signal (S315).

The position estimation unit 325 performs weighted averaging based onthe first weight parameter and the second weight parameter on the firstprovisional three-dimensional position and the second provisionalthree-dimensional position of the portable device 100, and estimates athree-dimensional position of the portable device 100 (S317).

The control unit 320 determines whether or not the three-dimensionalposition of the portable device 100 estimated through the weightedaveraging satisfies a predetermined criterion (S319). In a case wherethe predetermined criterion is satisfied (S319: Yes), the control unit320 causes the process to proceed to S321, and in a case where thepredetermined criterion is not satisfied (S319: No), the control unit320 ends the process.

In a case where the predetermined criterion is satisfied (S319: Yes),the control unit 320 performs operation control related to starting orstopping the engine, which is an example of the operation device 400(S321), and the control unit 320 ends the process.

The control example related to Example 2 has been described above.According to the control related to Example 2, the control device 300makes it possible to reduce the influence of the multipath, and canestimate a positional relationship between the portable device 100 andthe in-vehicle device 200 with higher accuracy.

In Example 1 and Example 2, an example has been described in which theposition estimation unit 325 calculates two weight parameters on thebasis of signals transmitted and received by each of the in-vehicledevice 200-1 and the in-vehicle device 200-2, and applies the weightparameters to a calculation process or a calculation result of apositional relationship between the portable device 100 and thein-vehicle device 200. As described above, by using a weight parameterbased on a reliability parameter, the influence of a calculation errordue to the multipath environment can be reduced. The control unit 320may select the in-vehicle device 200, which is less affected by themultipath environment, on the basis of the reliability parameterstransmitted and received by the in-vehicle device 200-1 and thein-vehicle device 200-2. Hereinafter, Example 3 will be described withreference to FIGS. 12 to 14 .

3.3. Example 3

FIG. 12 is an explanatory diagram for describing a control example ofthe system 1 related to Example 3. The control unit 320 related toExample 3 compares reliability parameters calculated on the basis ofsignals received from the portable device 100 by each of the pluralityof in-vehicle devices 200, and performs control for estimating apositional relationship on the basis of signals transmitted and receivedbetween the in-vehicle device 200 that has transmitted a signal that ismore appropriate as a processing target for estimating the positionalrelationship and the portable device 100. In the following description,a reliability parameter will be described as the reception power of asignal received by the antenna 221 but may be another reliabilityparameter described above.

For example, the antenna 221A-1, the antenna 221B-1, the antenna 221C-1and the antenna 221D-1 of the communication unit 220-1 included in thein-vehicle device 200-1 receive a Final signal from the antenna 121 ofthe communication unit 120 included in the portable device 100. Here, itis assumed that the reception power of the antenna 221A-1 is “−90 dBm”,the reception power of the antenna 221B-1 is “−95 dBm”, the receptionpower of the antenna 221C-1 is “−95 dBm”, and the reception power of theantenna 221D-1 is “−100 dBm”.

The antenna 221A-2, the antenna 221B-2, the antenna 221C-2 and theantenna 221D-2 of the communication unit 220-2 included in thein-vehicle device 200-2 receive a Final signal from the antenna 121 ofthe communication unit 120 included in the portable device 100. Here, itis assumed that the reception power of the antenna 221A-2 is “−99 dBm”,the reception power of the antenna 221B-2 is “−99 dBm”, the receptionpower of the antenna 221C-2 is “−101 dBm”, and the reception power ofthe antenna 221D-2 is “−101 dBm”.

In this case, the parameter calculation unit 321 calculates a basicstatistic based on the reliability parameter (for example, receptionpower) estimated for each antenna. The basic statistic may be, forexample, an average value, a maximum value, a minimum value, or a medianvalue.

For example, when the basic statistics are averaged, the parametercalculation unit 321 may calculate “−95 dBm” as an average value of thereception powers of the antenna 221A-1, the antenna 221B-1, the antenna221C-1, and the antenna 221D-1.

The parameter calculation unit 321 may calculate “−100 dBm” as anaverage value of the reception powers of the antenna 221A-2, the antenna221B-2, the antenna 221C-2, and the antenna 221D-2.

The position estimation unit 325 compares “−95 dBm” which is an averagevalue of the reception powers of the antenna 221A-1, the antenna 221B-1,the antenna 221C-1, and the antenna 221D-1 with“−100 dBm” which is anaverage value of reception powers of the antenna 221A-2, the antenna221B-2, the antenna 221C-2, and the antenna 221D-2.

The position estimation unit 325 selects the communication unit 220 thatis more appropriate (that is, highly reliable) as a processing targetfor estimating a positional relationship. For example, the positionestimation unit 325 may estimate a positional relationship between theportable device 100 and the in-vehicle device 200-1 on the basis of asignal transmitted and received between the communication unit 220-1including the antenna 221-1 having a greater average value of receptionpower and the communication unit 120 included in the portable device100.

The position estimation unit 325 may select three antennas out of fouror more antennas in each of the plurality of in-vehicle devices 200 onthe basis of a reliability parameter. The position estimation unit 325may compare reliability parameters calculated on the basis of signalsreceived by the respective three selected antennas. The positionestimation unit 325 may estimate a positional relationship between theportable device 100 and the in-vehicle device 200 on the basis of asignal transmitted and received between the in-vehicle device 200 thathas received a signal that is more appropriate as a processing targetfor estimating a positional relationship on the basis of a result of thecomparison and the portable device 100.

FIG. 13 is an explanatory diagram for describing another control exampleof the system 1 related to Example 3. For example, the antenna 221A-1,the antenna 221B-1, the antenna 221C-1, and the antenna 221D-1 of thecommunication unit 220-1 included in the in-vehicle device 200-1 receivea Final signal from the antenna 121 of the communication unit 120included in the portable device 100. Here, it is assumed that thereception power of the antenna 221A-1 is “−89 dBm”, the reception powerof the antenna 221B-1 is “−89 dBm”, the reception power of the antenna221C-1 is “−89 dBm”, and the reception power of the antenna 221D-1 is“−105 dBm”. In this case, the position estimation unit 325 may selectthe antenna 221A-1, the antenna 221B-1, and the antenna 221C-1 indescending order of the reception power.

The antenna 221A-2, the antenna 221B-2, the antenna 221C-2, and theantenna 221D-2 of the communication unit 220-2 included in thein-vehicle device 200-2 receive the Final signal from the antenna 121 ofthe communication unit 120 included in the portable device 100. Here, itis assumed that the reception power of the antenna 221A-2 is “−105 dBm”,the reception power of the antenna 221B-2 is “−90 dBm”, the receptionpower of the antenna 221C-2 is “−90 dBm”, and the reception power of theantenna 221D-2 is “−90 dBm”. In this case, the position estimation unit325 may select the antenna 221B-2, the antenna 221C-2, and the antenna221D-2 in descending order of the reception power.

In a case where each of the plurality of in-vehicle devices 200 has N(where 4≤N) antennas, the position estimation unit 325 may select M(where 3≤M≤N) antennas out of the N antennas in each of the plurality ofin-vehicle devices 200 on the basis of a reliability parameter.

Subsequently, the position estimation unit 325 compares reliabilityparameters calculated on the basis of signals received by the respectivethree antennas selected for each of the in-vehicle device 200-1 and thein-vehicle device 200-2.

In a case where a method of comparing reliability parameter averagevalues of the respective antennas 221 is used, the position estimationunit 325 acquires a comparison result that the average reception powerof the antenna 221A-1, the antenna 221B-1, and the antenna 221C-1 of thein-vehicle device 200-1 is higher than that of the antenna 221B-2, theantenna 221C-2, and the antenna 221D-2 of the in-vehicle device 200-2and a signal that is more appropriate as a processing target forestimating a positional relationship has been transmitted and received.

The position estimation unit 325 executes a process of estimating apositional relationship between the portable device 100 and thein-vehicle device 200-1 on the basis of signals transmitted and receivedbetween the in-vehicle device 200-1 that has transmitted and receivedthe signal that is more appropriate as a processing target forestimating a positional relationship and the portable device 100. Thepositional relationship between the portable device 100 and thein-vehicle device 200-1 may be an arrival angle of a signal or may be atwo-dimensional position or a three-dimensional position of the portabledevice 100 as in Example 1 and Example 2.

The position estimation unit 325 may select, from each of the pluralityof in-vehicle devices 200, an antenna of which a reliability parameterbased on a received signal satisfies a specified criterion among four ormore antennas of each of the plurality of in-vehicle devices 200. Forexample, the position estimation unit 325 may select, from each of theplurality of in-vehicle devices 200, an antenna of which a reliabilityparameter based on a received signal is a predetermined value among thefour or more antennas of each of the plurality of in-vehicle devices200. More specifically, for example, in a case where a reliabilityparameter is the reception power and a predetermined value is −90 dBm,the position estimation unit 325 may select an antenna in which thereception power of a received signal is equal to or more than −90 dBmamong the four or more antennas. The position estimation unit 325 maycompare reliability parameters of the selected antennas by each of theplurality of in-vehicle devices 200.

Example of Operation Process

FIG. 14 is an explanatory diagram for describing an example of anoperation process of the system 1 related to Example 3. In the followingdescription, an operation process in a case where the reliability of atransmitted and received signal becomes higher as a value of areliability parameter becomes smaller will be described. First, thecommunication unit 120 included in the portable device 100 transmits aPoll signal, and the communication unit 220-1 included in the in-vehicledevice 200-1 and the communication unit 220-2 included in the in-vehicledevice 200-2 receive the Poll signal (S401).

Subsequently, the communication unit 220-1 and the communication unit220-2 transmit a Resp signal as a response to the Poll signal, and thecommunication unit 120 receives the Resp signal (S403).

The communication unit 120 transmits a Final signal as a response to theResp signal, and the communication unit 220-1 and the communication unit220-2 receive the Final signal (S405). Here, the communication unit220-1 and the communication unit 220-2 transmit various types ofinformation regarding the transmitted and received signals to thecommunication unit 310 included in the control device 300.

Subsequently, the position estimation unit 325 calculates a firstdistance measurement value on the basis of the signals transmitted andreceived between the portable device 100 and the in-vehicle device200-1, and calculates a second distance measurement value on the basisof the signals transmitted and received between the portable device 100and the in-vehicle device 200-2 (S407).

Subsequently, the parameter calculation unit 321 calculates a firstreliability parameter on the basis of the signal received by thein-vehicle device 200-1, and calculates a second reliability parameteron the basis of the signal received by the in-vehicle device 200-2(S409).

The control unit 320 determines whether or not the reliability parameterbased on the signal received by the in-vehicle device 200-1 is largerthan the reliability parameter based on the signal received by thein-vehicle device 200-2 (S413). In a case where the reliabilityparameter based on the signal received by the in-vehicle device 200-1 islarger (S413: Yes), the control unit 320 causes the process to proceedto S415, and in a case where the reliability parameter based on thesignal received by the in-vehicle device 200-2 is larger (S413: No), thecontrol unit 320 causes the process to proceed to S419.

In a case where the reliability parameter based on the signal receivedby the in-vehicle device 200-1 is larger (S413: Yes), the positionestimation unit 325 estimates an arrival angle of a signal on the basisof the signal transmitted and received by the communication unit 220-2included in the in-vehicle device 200-2 (S415).

The position estimation unit 325 estimates a three-dimensional positionof the portable device 100 on the basis of the estimated arrival angleof the signal and the second distance measurement value (S417).

In a case where the reliability parameter based on the signal receivedby the in-vehicle device 200-2 is larger (S413: No), the positionestimation unit 325 estimates an arrival angle of a signal on the basisof the signal transmitted and received by the communication unit 220-1included in the in-vehicle device 200-1 (S419).

The position estimation unit 325 estimates a three-dimensional positionof the portable device 100 on the basis of the estimated arrival angleof the signal and the second distance measurement value (S421).

The control unit 320 determines whether or not the estimatedthree-dimensional position of the portable device 100 satisfies apredetermined criterion (S423). In a case where the predeterminedcriterion is satisfied (S423: Yes), the control unit 320 causes theprocess to proceed to S425, and in a case where the predeterminedcriterion is not satisfied (S423: No), the control unit 320 ends theprocess.

In a case where the predetermined criterion is satisfied (S423: Yes),the control unit 320 performs operation control related to starting orstopping the engine, which is an example of the operation device 400(S425), and the control unit 320 ends the process.

An example of an operation process of the system 1 related to Example 3has been described above. An operation process in a case where there area plurality of in-vehicle devices 200 is not limited to the aboveexample. For example, after a Poll signal, a Resp signal, and a Finalsignal are transmitted and received between the communication unit 120included in the portable device 100 and the communication unit 220-1included in the in-vehicle device 200-1, a Poll signal, a Resp signal,and a Final signal may be transmitted and received between thecommunication unit 120 and the communication unit 220-2 included in thein-vehicle device 200-2. The position estimation unit 325 may estimate afirst three-dimensional position of the portable device 100 on the basisof the signals transmitted and received between the portable device 100and the in-vehicle device 200-1, and estimate a second three-dimensionalposition of the portable device 100 on the basis of the signalstransmitted and received between the portable device 100 and thein-vehicle device 200-2, and then the control unit 320 may comparereliability parameters. For example, in a case where it is determinedthat the in-vehicle device 200-1 has transmitted and received a signalhaving higher reliability than the in-vehicle device 200-2, the controlunit 320 may set the first three-dimensional position as athree-dimensional position of the portable device 100.

According to the control related to Example 3 described above, thecontrol device 300 can estimate a positional relationship between theportable device 100 and the in-vehicle device 200 with higher accuracyby selecting the in-vehicle device 200 having a smaller influence ofmultipath.

Although the details of Example 1, Example 2, and Example 3 have beendescribed, the control device 30 according to the present embodiment mayperform control by combining the above Example 1 with one of Example 2or Example 3.

In a case where Example 1 is combined with Example 2, for example, theposition estimation unit 325 performs weighted averaging using a weightparameter based on a reliability parameter on an inter-antenna phasedifference of antenna pair of the in-vehicle device 200-1. The positionestimation unit 325 estimates an arrival angle of a signal and aprovisional three-dimensional position of the portable device 100 on thebasis of the inter-antenna phase difference subjected to the weightedaveraging. The position estimation unit 325 estimates a arrival angle ofa signal and a provisional three-dimensional position of the portabledevice 100 through the same process in the in-vehicle device 200-2. Theposition estimation unit 325 may perform weighted averaging based on areliability parameter on the estimated two provisional three-dimensionalpositions of the portable device 100 to estimate a three-dimensionalposition of the portable device 100.

In a case where Example 1 is combined with Example 3, for example, theposition estimation unit 325 compares respective reliability parametersof the in-vehicle device 200-1 and the in-vehicle device 200-2, andselects the in-vehicle device 200 for estimating a positionalrelationship with the portable device 100 according to a result of thecomparison. Next, the position estimation unit 325 performs weightedaveraging using a weight parameter based on a reliability parameter onthe inter-antenna phase difference of the antenna pair of the selectedin-vehicle device 200. The position estimation unit 325 may estimate anarrival angle of a signal and a three-dimensional position of theportable device 100 on the basis of the inter-antenna phase differencesubjected to the weighted averaging.

According to the control in combination between Example 1 and one ofExample 2 or Example 3 described above, the control device 30 canestimate a positional relationship between the portable device 100 andthe in-vehicle device 200 with higher accuracy.

4. Appendix

Although the preferred embodiments of the present invention have beendescribed in detail with reference to the accompanying drawings, thepresent invention is not limited to these examples. It is clear that aperson skilled in the art can conceive of various changes ormodifications within the scope of the technical ideas disclosed in theclaims, and these are also naturally understood to belong to thetechnical scope of the present invention.

For example, the series of processes by each device described in thepresent specification may be realized by using any of software,hardware, and a combination of software and hardware. A program formingthe software is stored in advance in, for example, a recording medium(non-transitory media) provided inside or outside each device. Eachprogram is read into a RAM at the time of execution by a computer andexecuted by a processor such as a CPU. The recording medium is, forexample, a magnetic disk, an optical disc, a magneto-optical disc, or aflash memory. The above computer program may be distributed via, forexample, a network instead of using a recording medium.

The steps in the processing of the operation of the system 1 accordingto the present embodiment do not necessarily have to be processed in atime series according to the order described as the explanatory diagram.For example, each step in the processing of the operation of the system1 may be processed in an order different from the order described in theexplanatory diagram, or may be processed in parallel.

What is claimed is:
 1. A control device comprising: a control unit thatperforms control for estimating a positional relationship between aplurality of communication devices each having three or more antennasand another communication device on the basis of signals transmitted andreceived between the plurality of communication devices and the othercommunication device, wherein the control unit compares reliabilityparameters that are indexes indicating a degree of whether or not asignal is appropriate as a processing target for estimating a positionalrelationship between each of the plurality of communication devices andthe other communication device, calculated on the basis of the signalsreceived from the other communication device by the communicationdevice, and performs control for estimating the positional relationshipon the basis of a signal transmitted and received between thecommunication device that has received a signal that is more appropriateas a processing target for estimating the positional relationship andthe other communication device.
 2. The control device according to claim1, wherein the control unit compares basic statistics based onreliability parameters estimated for the respective three or moreantennas or for respective antenna pairs of each of the plurality ofcommunication devices, and performs control for estimating thepositional relationship on the basis of a signal transmitted andreceived between the communication device that has received a signalthat is more appropriate as a processing target for estimating thepositional relationship, determined on the basis of a result of thecomparison, and the other communication device.
 3. The control deviceaccording to claim 2, wherein the basic statistics include at least oneof an average value, a maximum value, a minimum value, and a medianvalue.
 4. The control device according to claim 1, wherein the three ormore antennas are four or more antennas, and the control unit selectsthree antennas out of the four or more antennas from each of theplurality of communication devices on the basis of the reliabilityparameters, compares the reliability parameters calculated on the basisof the signal received by each of the three selected antennas, andperforms control for estimating the positional relationship on the basisof a signal transmitted and received between the communication devicethat has received a signal that is more appropriate as a processingtarget for estimating the positional relationship on the basis of aresult of the comparison and the other communication device.
 5. Thecontrol device according to claim 1, wherein the three or more antennasare four or more antennas, and the control unit selects an antenna inwhich the reliability parameter satisfies a specified criterion amongthe four or more antennas from each of the plurality of communicationdevices, compares reliability parameters for the plurality of respectivecommunication devices, calculated on the basis of a signal received byeach of the selected antennas, and performs control for estimating thepositional relationship on the basis of a signal transmitted andreceived between the communication device that has received a signalthat is more appropriate as a processing target for estimating thepositional relationship on the basis of a result of the comparison andthe other communication device.
 6. The control device according to claim1, wherein the control unit estimates an arrival angle of the signalreceived by the communication device from the other communication deviceas the positional relationship between the communication device and theother communication device.
 7. The control device according to claim 5,wherein the control unit estimates a two-dimensional position or athree-dimensional position of the other communication device as thepositional relationship between the communication device and the othercommunication device on the basis of the arrival angle of the signal. 8.The control device according to claim 1, wherein the reliabilityparameters include at least one of an index indicating a magnitude ofnoise of a signal received by at least one of the communication deviceand the other communication device, or an index indicating a validitythat the signal is based on a direct wave.
 9. The control deviceaccording to claim 1, wherein the communication device is mounted on amoving object.
 10. The control device according to claim 9, wherein theother communication device is carried by a user who is using the movingobject.
 11. The control device according to claim 1, wherein the signalsinclude a wireless signal compliant with ultra-wideband wirelesscommunication.
 12. A system comprising: a plurality of communicationdevices each of which has three or more antennas; another communicationdevice that has one or more antennas; and a control device that performscontrol for estimating a positional relationship between the pluralityof communication devices and the other communication devices on thebasis of signals transmitted and received between the plurality ofcommunication devices and the other communication devices, wherein thecontrol device compares reliability parameters that are indexesindicating a degree of whether or not a signal is appropriate as aprocessing target for estimating a positional relationship between eachof the plurality of communication devices and the other communicationdevice, calculated on the basis of the signals received from the othercommunication device by the communication device, and performs controlfor estimating the positional relationship on the basis of a signaltransmitted and received between the communication device that hasreceived a signal that is more appropriate as a processing target forestimating the positional relationship and the other communicationdevice.
 13. A control method executed by a computer, comprising:transmitting and receiving signals between a plurality of communicationdevices each of which has three or more antennas and anothercommunication device; and performing control for estimating a positionalrelationship between the plurality of communication devices and theother communication device on the basis of the transmitted and receivedsignals, wherein the performing control for estimating a positionalrelationship between the plurality of communication devices and theother communication device includes comparing reliability parametersthat are indexes indicating a degree of whether or not a signal isappropriate as a processing target for estimating a positionalrelationship between each of the plurality of communication devices andthe other communication device, calculated on the basis of the signalsreceived from the other communication device by the communicationdevice, and performing control for estimating the positionalrelationship on the basis of a signal transmitted and received betweenthe communication device that has received a signal that is moreappropriate as a processing target for estimating the positionalrelationship and the other communication device.